How to use it
- Open the page; the clock syncs automatically.
- Read the exact time, date, week number and time zone.
- Check whether your device clock is fast or slow.
- Click Measure again after your computer wakes from sleep.
How the clock is synced
Your computer or phone keeps its own time, and it can drift by seconds, especially after sleep or on devices that rarely sync. This page doesn't simply show your device clock. It asks our server for the time several times in a row, the way network time protocols do:
- It records when each request left and when the answer came back.
- It keeps the fastest round trip, because that one had the least network delay.
- It assumes the answer took half of that round trip to arrive and corrects for it.
The result is shown with a precision value, typically a few dozen milliseconds on a normal connection. The page re-measures when you switch back to the tab, so a laptop that just woke up gets corrected too.
The time zone comes from your browser settings. If it looks wrong, check the date and time settings on your device.
Is my clock fast or slow?
Below the clock you'll see how your device time compares with the synced time, for example Your device clock is 1.4 seconds fast. If the difference is inside the measurement precision, the page says your clock is accurate.
To fix a clock that is off:
- Windows: Settings > Time & language > Date & time, turn on Set time automatically and click Sync now.
- macOS: System Settings > General > Date & Time, turn on Set time and date automatically.
- iPhone and Android: turn on automatic date and time in the Settings app.
A second or two rarely matters, but it does when you are trying to buy concert tickets at a release time, join an auction, or start a meeting on the dot.
Daylight saving time in the United States
Most of the US moves clocks twice a year under the Energy Policy Act of 2005:
| Change | When | What happens |
|---|---|---|
| DST starts | Second Sunday in March, 2:00 a.m. | Clocks spring forward to 3:00 a.m. |
| DST ends | First Sunday in November, 2:00 a.m. | Clocks fall back to 1:00 a.m. |
Hawaii and most of Arizona stay on standard time all year, and so do Puerto Rico, Guam, the U.S. Virgin Islands and American Samoa. The page works out the next change for whatever time zone your browser reports, so it also works in Europe, Australia or anywhere else, and tells you if your zone has no clock change at all.
US time zones at a glance
| Time zone | Standard time | Daylight time | Example cities |
|---|---|---|---|
| Eastern | UTC−5 (EST) | UTC−4 (EDT) | New York, Atlanta, Miami |
| Central | UTC−6 (CST) | UTC−5 (CDT) | Chicago, Dallas, Houston |
| Mountain | UTC−7 (MST) | UTC−6 (MDT) | Denver, Salt Lake City; Phoenix stays on MST |
| Pacific | UTC−8 (PST) | UTC−7 (PDT) | Los Angeles, Seattle, Las Vegas |
| Alaska | UTC−9 (AKST) | UTC−8 (AKDT) | Anchorage |
| Hawaii | UTC−10 (HST) | not observed | Honolulu |
The world clock section on the page shows New York, Chicago, Denver, Los Angeles, London and Tokyo side by side. For other cities use the time zone converter.
Week numbers
Under the date you'll see the current week number. It follows ISO 8601, the international standard used in business planning and many calendars: weeks start on Monday, and week 1 is the week that contains the year's first Thursday. Some US calendars number weeks differently (starting on Sunday, with week 1 containing January 1), so the two systems can differ by one around the new year. The week number tool shows the ISO week for any date.
Frequently asked questions
How accurate is this clock?
The page shows the measured precision under the clock, usually a few dozen milliseconds. It depends on how fast and stable your connection is; the fastest of several round trips is used.
Why is my computer clock wrong?
Device clocks drift over time and may not resync after sleep, a dead battery or a time zone change. Turning on automatic time in your system settings usually fixes it.
When do the clocks change in the US?
Daylight saving time starts on the second Sunday in March at 2:00 a.m. and ends on the first Sunday in November at 2:00 a.m. The page shows the exact date of the next change for your time zone.
Does Arizona observe daylight saving time?
Most of Arizona does not and stays on Mountain Standard Time (UTC−7) all year. The Navajo Nation in northeastern Arizona does observe it.
Which time zone does the page use?
The one your browser reports, which normally matches your device settings. The full name and UTC offset are shown under the date.
Sources
Last updated: November 12, 2026